1. Field of the Invention
The present invention relates to a weighing apparatus and method for the rapid and accurate weighing of items moving along a packaging or assembly line.
2. Description of the Prior Art
The weighing of items produced during the manufacturing process to assure that the weight of the produced item meets with the weight specifications for the product is a vital and necessary task in many industries. This is especially true in the food, pharmaceutical, and cosmetics industries where the weights of the products are typically inspected by the FDA, USDA or other governmental agency. Many manufacturing lines in these industries produce items at a rate of 30 or more items per minute making the speed of the weighing process critical.
Due to the need for accurate weighing of the product by the manufacturer, and the need to maintain a relatively rapid production line, many manufacturers rely on statistical sampling methods in order to estimate the average weight of the product. These statistical sampling methods typically include manually placing the product on a platform balance which has been calibrated to NIST standards and taking a weight reading once the platform balance is sufficiently stable. By sampling a sufficiently large population of the produced items, an average weight and a standard deviation is determined. However, statistical sampling does not inspect a 100% of the items produced and the process is relatively slow. Also, in most cases where statistical sampling is employed, the weighings are performed outside the manufacturing area and as a result, the items sampled must typically be destroyed in order to prevent the possibility of contamination.
Statistical weight sampling is also currently performed using automated means. These methods typically require robotic or mechanical diversion of the items to be sampled from the manufacturing line to a weighing station away from the line where they are weighed. The traditional process for weighing items using automated means typically include (1) convey the item from the manufacturing line to a weigh station, (2) tare the weighing apparatus, (3) position the item on the weigh station, (4) wait for a stable weight reading, (5) record the weight reading, (6) remove the item from the weigh station, and (7) convey the item back to the manufacturing line. Due to the length of time it takes to perform a weight reading, these automated methods typically are not fast enough to perform an inspection of a 100% of the items produced.
High speed check weighing processes are also currently being used in order to weigh items on a production line. These high speed check weighing processes generate a weight reading while the items are in motion. However, since these weight readings are acquired while the items are in motion, the resulting weight measurements are not traceable to NIST standards. Furthermore, these high speed check weighing procedures are typically limited in the minimum and maximum weights that can be weighed, and they are also limited in the weight resolution that can be achieved.
Accordingly, there is a need for a weighing apparatus and method rapid enough to operate at production rate line speeds in order to allow the weighing of 100% of the items produced for release.
Accordingly there is also a need for a weighing apparatus and method which can be done in line while the items remain on the manufacturing line eliminating the need to divert the items to a weighing station away from the manufacturing line.
Accordingly, there is also a need for a weighing apparatus and method that is accurate and capable of being NIST certified.
The present invention is a weighing apparatus and method for the rapid and accurate weighing of items moving along on a packaging or assembly line.
As will be described in greater detail hereinafter, the present invention solves the aforementioned and employs a number of novel features that render it highly advantageous over the prior art.
Accordingly, it is an object of this invention to provide a weighing apparatus and method rapid enough to operate at production rate line speeds in order to allow the weighing of 100% of the items produced for release.
Accordingly, it is also an object of this invention to provide a weighing apparatus and method which can be performed in line while the items remain on the manufacturing line eliminating the need to divert the items to a weighing station away from the manufacturing line.
Accordingly, it is a further object of this invention to provide a weighing apparatus and method that is accurate and capable of being NIST certified.
To achieve these objectives, and in accordance with the purposes of the present invention the following weighing apparatus and method for the repeated rapid and accurate weighing of items moving along on a packaging or assembly line is presented.
The apparatus and method for weighing relies on a weighing assembly that is physically fixed in place with no moving parts upon which a weighing transducer is attached. The weighing transducer is secured onto a fixed base. The fixed base is positioned in order to allow the weighing transducer to rest securely over the conveyance means. Since the fixed base does not move, the weighing transducer is able to take weight readings with minimal motion related instability. The weighing transducer is preferably a load cell or a plurality of load cells.
A holding device is operatively coupled to the weighing transducer allowing the weighing transducer to accurately weigh any item freely suspended from the holding device. The conveyance means works synchronously with the holding device in order to obtain an accurate weight reading. The conveyance means delivers the item to be weighed to the holding device that in turn captures the item. Once the item is conveyed to the holding device, the conveyance means then stops. The item is captured by the holding device, immediately followed by the lowering of the conveyance means to a height sufficient to enable the item to be suspended freely on the holding device, typically a distance of less than 0.1 inch. With the item suspended on the holding device, the weighing transducer is able to take an accurate measurement of the weight of the item. Once the item is weighed the conveyance means rises, the weighed item is then released by the holding device and conveyed away from the holding device while another item is conveyed to the holding device.
The method for weighing items starts with first taking a no load weight reading while conveying an item to the holding device. Once the item is at the holding device, the conveyance means is then stopped. The item is captured by the holding device and the conveyance means is lowered allowing the item captured on the conveyance base to be suspended with only the weighing transducer supporting the holding device and the captured item. The weight reading is then performed with the item as the load. After the weight reading is performed the conveyance base is raised to its initial height so that the item is no longer suspended on the holding device. The item is released by the holding device and the item is conveyed away while another item is conveyed to the holding device.
This process eliminates the need to tare the weighing apparatus, a necessary step in the prior art. The weight readings taken by the weighing transducer is digitally sent to a monitoring processor means which first takes the no load reading and subtracts that to the subsequent load readings which then results in the weight of the item. The weight of the item is then available to transcribe to a report or to utilize in order to determine whether the item passes weight requirements.
The entire weighing process takes less than a second to complete. Repeatable weight readings having a resolution of 0.01 grams are taken within 0.1 seconds. Also, by employing multiple apparatuses in tandem, even higher throughput can be achieved. Consequently, the weighing process can be put directly in line with the normal manufacturing process without slowing down the manufacturing process, and enabling a 100% of the items produced to be weight sampled.
Other objects, features, and advantages of the invention will become more readily apparent upon reference to the following description when taken in conjunction with the accompanying drawings.